Fractionation of oils by selective extraction



June I, 1965 P. A. GROLL 3,186,938

FRACTIONATION OF OILS BY SELECTIVE EXTRACTION Filed May 18, 1961 2 Sheets-Sheet 1 COMP.

28 STPJP SOLVENT TANK 224 (MORE VOLATIL CONSTITUENTS) a TANK DEPHLEGMATDR a; 3 26 1 0 y 8 l7: l7 2? V I a m3 [m3 #8 HEAT I 0 0 0 0 i i 19a. 2/ I l9 1 0 MIXER. i OLER ROD, T PRODUCT I- ACTISN ,QAIIEK l5 9 29 FACTION E 2 G EXTRACTION SOLVENT TANK (LESS VOLATIL j\ CONSTITUENTSJ 8a "L @J 7 TANK i p aoguc-r INVENT OR FACTION F CT PRODUCT PACTION F FACTION HERBERT F. A. GROLL 1:1 1

June 1965 H. P. A. GROLL 3,186,938

' FRACTIONATION 0F OILS BY SELECTIVE EXTRACTION I Filed May 18; 1961 2 Sheets-Sheet 2 PRODUCT FACTION DUCT PRODUCT PRO INVENTOR HERBERT I? A. emu.

United States Patent 3,186,938 FRACTIONATION OF 0E8 BY SELECTIVE EXTRACTION Herbert P. A. Groli, Skogsvagen 18, Pixbo, Sweden Filed May 18, 1%1, Ser. No. 111,114 Claims priority, application Sweden, Aug. 24, 1953, 7,619/53, 7,620/53 7 Claims. (Cl. 208-316) This invention is concerned with an improvement of the method for fractionating soluble mixtures of relatively high molecular organic substances by solvent extraction with homogeneous solvent mixtures consisting of at least one relatively less volatile and at least one relatively more volatile constituent, the selectivity of the solvent mixture being a function of the operating temperature, which is chosen so that an extract phase and a residue phase are formed, the recovery of bulk of the pure solvent mixture from the extract phase for reuse in at least one extraction zone being carried out by precipitating from the extract a liquid phase containing the material extracted together with relatively little solvent. Preferably but not necessarily the operating temperature is beyond the critical temperature of the more volatile solvent constituent.

It is also preferred to use the method in a plant wherein a multiplate countercurrent effect can be achieved by providing at least one fractionating column equipped with means for applying countercurrent and reflux and for enhancing the mutual contact between both liquid phases.

Solvent mixtures of the above described type have been suggested among other solvents that it has been further suggested to adjust the selectivity of the solvent mixture by regulating the operating temperature only. A temperature gradient may be applied along the column. As an example a mixture of methane and butane has been suggested.

If a plant is operated using a mixture of butane and methane or similar mixtures of the type described above, the fractionation actually achieved always is found to be very much less effective than expected or calculated. The real reason for this peculiarity has hitherto been unknown, but on account of these unexpected and unexplained difficulties the preferred practice has been to fractionate oils by solvent extraction with solvent-s consisting either of chemical entities such as propane or butane or with solvent mixtures constituting relatively narrow cuts, for instance a technical butane-propane fraction, propanepropylene, and the like.

If the selectivity of these solvents is adjusted to the value required by regulating the operating temperature, crude oil residues, lubricating oil cuts, and glycerides can be fractionated quite effectively. However, if it is attempted to fractionate light oils such as higher free fatty acids obtained by splitting natural oils and fats, tall oil, or hydrocarbons of moderate molecular weight, the operating temperature becomes very near the critical temperature of the solvent, and within a few degrees centigrade either all the oil becomes soluble or it becomes prac tically insoluble. In other words the temperature range of limited solubility, the only one within which a sufiicient selectivity can be expected, becomes so narrow as to make the process practically inoperable.

It has now been found that the inferior fractionating results with the first mentioned solvent mixtures consisting of a less and of a more volatile constituent are caused by the fact that there occurs not only a desirable segregation of the oil to be fractionated, but also a very undesirable segregation of the solvent mixture. This upsets the operation of the plant. In detail this phenomenon is explained as follows:

In the fractionating column and in the accessory precipitator and separator two liquid phases are formed, one

3,186,938 Patented June 1, 1965 'ice of which is rich in solvent, usually 70-90% for the eX- traet phase in the column and 96-100% for the recovered solvent phase in the separator, while the other phase contains considerably more of the oil constituents, usually around 50% or more, and thus relatively less solvent mixture than the solvent rich phase. The solvent mixture recovered by distillation from the various types of oil rich phase has a composition entirely different from that of the corresponding solvent rich phase. It contains very little, sometimes practically none, of the more volatile solvent constituent. The oil rich phases occurring in different parts of the plant may partly be used as reflux but eventually they are withdrawn from the plant for recovery of the various oil fractions. Thereby the composition of the balance of the solvent mixture remaining in circulation in the plant is changed. It will contain lower and lower percentages of the less volatile constituent and its solvent power will therefore diminish gradually. However, as the solvent is continuously recovered from the fractions withdrawn and as this recovered solvent is returned to the solvent mixture circulating in the plant an equilibrium condition should eventually be achieved and, at least theoretically, the composition of the circulating solvent, while it may not be identical with the original composition, ought to be quite constant.

In practice, however, it has been found that stable conditions never can be achieved in this manner. As soon as the plant is put on stream the composition of the solvent mixture is upset temporarily and, instead of returning to steady conditions gradually, it will fluctuate periodically for hours. The lengths of the time periods of these fluctuations observed are a function of the ratio of the liquid holdup of the plant to the pumping rate for the recirculation of the solvent mixture. Zones of different solvent composition are pumped around in the plant following one another. While very rough fractionations, such as deasphaltizing, might be carried out with a plant in such a fluctuating condition, it is quite impossible to achieve any accurate fractionation. Furthermore, if during the operation of the plant conditions such as reflux ratio, rate of feed, and/ or of withdrawal of the fractions are changed, new fluctuations of the type described immediately occur and persist for a long time in the manner described.

Now a method has been devised for avoiding the difiiculties described so that soluble, relatively high molecular organic material can be fractionated accurately by solvent extraction with a homogeneous solvent mixture, consisting of at least one at the operating pressure and temperature liquid less volatile constituent and at least one substantially more volatile constituent, said solvent mixture possessing such a selective solvent power that an extract phase and a residue phase are formed, while recovering for reuse the substantially pure solvent mixture from the extract phase by precipitating therefrom the extracted constituents of said organic material. The improvement constituting the present invention comprises adjusting the selectivity of the solvent to the value desired by maintain-ing a suitable time-constant temperature and by maintaining a time-constant desired composition of the solvent mixture in a fractionating zone by adding at least at one point of the solvent mixture cycle, but outside of the fractionating zone further quantity of a more volatile solvent constituent and at another point of the solvent mixture cycle outside the fractionating zone withdrawing the same volatile constituent at such rates of addition and withdrawal that after the adding and/or withdrawing operation the percentage of the more volatile constituent of the solvent mixture becomes the desired one for the :fractiona'ting zone in which the solvent mixture is to be re-used.

The location and the order of application of the points ,3 v of withdrawal and addition of the more volatile constituent within the solvent cycle are immaterial for the efiect of the arrangement in preventing fluctuations of the composition. However, it is preferred in all cases in which no other reasons callfor a different order, to arrange the point of addition before the point'of withdrawal and to utilize at :least one portion of the solvent cycle lying between both ated at a constant temperature and pressure the latter being held constant by an automatically controlled release valve adjusted for maintaining the desired pressure. The valve will then release the more volatile constituent in the gaseous state at a rate automatically varying with the fluctuating composition of the solvent entering the stripper, but the solvent discharged from the stripper shall always have the same composition determined by the temperature and pressure at which the operaltion of the stripper has been fixed. Instead of holding the rate of addition of the more'volatile constituent constant and automaltically adjusting the rate of withdrawal as described above, the opposite may be done, i.e the gaseous constituent enters a 'saturator in which'the extract is saturated through a reducing valve which keeps the saturating pressure in the satur-a-tor constant While the operating temperature is also held constant, and then the more volatile constituent is withdrawn as gas from the stripper at a constant rate.

It is to be understood that the use of this invention is not restricted to frao'tionating fatty acids and other substances of moderate molecular weight which, as mentioned above, cannot be satisfactorily fractionated by using propane or similar solvents possessing a too narrow temperature Zone of seledtivity at the high operating tem perature.

The invention can be used with advantage for fractionating any type of mixtures of organic substances, provided they are limitedly soluble in any of the solvent mixtures which can be chosen for the purpose. For instance the substances enumerated below can be fractionated according to this invention: petroleum, its higher fractions and distillation residues, such as topped crudes, and especially, short residues, as well as tar oils, shale oils, and synthetic hydrocarbon oils such as Fischer-Tropsch products, products of coal hydrogenation, and products ,tained'by polymerizing hydrocarbons and certain substituted hydrocarbons. A further group of materials which can with special advantage be fractionated according to this'invention comprises natural fats and oils of animal and vegetable origin i.e. glycerides, fatty acids and 'mixtures of these substances with natural resins and resinic acids eg/ crude tall oil or tall oil fatty acids as Well as crude mixtures of fatty acids such as may be obtained by refining of fats and oils, by hydrolyzing fats and oils, and by oxidation of paralfin wax. Other mixtures suitable for being fractionated according to this invention are essential oils, terpenes, 'rosins, rosin oils, etc. as well as polymerized oils and soluble types of artificial resin-s eg. stand oils, boiled linseed oil-s, alkyd resins, modified alkyds, polyester resins, and certain modified epoxy and phenol resins, polyvinyl esters and ethers, polyacrylates and methacrylates and various kinds of e c-polymers.

A special advantage when using this invention resides in the fact that the selective solvent combination can be chosen without any risk for the detrimental fluctuating effect otherwise caused by the segregation of solvent mixtures of constituents with widely difiering volatilities.

Suitable pairs of solvents and modifying gases are for instance, butane and ethane,'propane and methane, gasoline and propane, liquid carbon dioxide and nitrogen, carbon dioxide and nitrous oxide (providing nonflammable mixtures are to be fractionated),,difiuoro-dichloromethane and carbon dioxide, sulfur dioxide and nitrous oxide.

Even other homogeneous solvent. mixtures can be used consisting of at least one less volatile liquid constituent and one substantially more -vol-atile constituent which, however, can be in the liquid state too under the conditions prevailing in the fractionating zone. Thus the more volatile constituent may be added at the point of addition as a liquid. For instance, liquid carbon dioxide may be used as the more volatile constituent and propane, butane, methanol, or acetoneas the less volatile constituent.

In order to make this invention more clear in the following two types of plant are described which are suitable for reducing the present invention to practice. However, it is to be understood that it is not my intention to limit my invention to the specific apparatus or the substances and/or solvents used in the examples.

A flow sheet of a one-column plant for carrying out this invention is shown in FIG. 1. The oil is pumped from tank 1 by pump 2 into column 6 and is there contacted with the practically oil-free solvent mixture entering through line 7 as light phase. The extract formed by the countercurrent contact in the lower part of column 6 proceeds as light phase through the upper part of column 6 in countercurrent contact with the reflux of heavy phase entering through valve 15.

The extract thus rectified is pumped by pump 8 to mixer 9 where it is mixed with the more volatile solvent constituent entering through valve 10 from the pressure storage tank 11. This is dissolved instantly and precipitates at least part of the oil constituents from the extract. Should this precipitation he insufiicient, the

7 suspension of precipitate in the solvent mixture can be heated in heater 12 whereby the precipitation is completed. The precipitated heavy phase is separated from the light solvent phase in separator 13. Part of the heavy phase is cooled in cooler 14, if so desired, to the operating temperature of column 6 and refluxed to this column by valve 15. i

Another part of the precipitate is expanded through valve 16 into evaporator 17 which is heated by steam coil 18 and operated under a pressure 'sufiicient for producing a liquid distillate in the dephlegmating receiver 7 20. The evaporation residue is withdrawn through valve 19 and collected as product fraction F The vapors leaving evaporator 17 enter dephlegmator 20 wherein a liquid phase is condensed out which through valve 21 is withdrawn to tank 4 where the relatively less volatile solvent constituent is kept. The more volatile gaseous constituent of the solvent proceeds to tank 23. From this tank the gas is withdrawn by compressor 24 to tank 11, where the relatively more volatile solvent constituent is kept. r

The solvent mixturesubstantially freed from oil in sepaartor 13 as described, proceeds through valve 25 to stripper 26. On the'way to this stripper it is blended with less volatile solvent constituent pumped from tank '4 by pump 5 through valve 3 at such a'rate'as is necessary for keeping the extraction cycle of the plant filled with the appropriate amount of liquid so that a liquidgas interface is maintained in the lower part of stripper 26. constituent pumped by pump 5 at the above defined rate may be blended through valve 3a into the oil feed to column 6. 7 it" By proper adjustment of the heating means, 27 and of valve 28 so much of the gas is removed from the sol vent mixture that the latter after cooling in cooler 29 will possess the composition chosen for operation of column 6. Thereby the solvent power and the selec tivity of the solvent with respect to the various c'onstit-' Alternatively the relatively less volatile solvent uents of the oil are adjusted and accurately maintained at a predetermined value irrespective of the rates of withdrawal and of the percentages of solvent in the precipitate and in the residue leaving the fractionating equipment through valves 16 and 31) respectively. The extraction residue which is withdrawn from column 6 by valve 30 is freed from solvent in the evaporator 17a and eventually withdrawn through valve 19a as product fraction F The solvent vapors from evaporator 17a are treated and their constituents recycled by 20a, 21a, and 22a respectively in a manner exactly analogous to that described for the vapors emerging from evaporator 17.

A multi-column plant with 3 columns is shown in FIG. 2. The oil to be fractionated is pumped from tank 53 by pump 52 into the mixer 55 where it is prediluted with as much of the less volatile constituent of the solvent mixture pumped by pump 54 from tank 51 as is necessary to maintain a sufficient volume of liquid in the circulating system. This solution of solvent in oil contains approximately the same percentage of solvent as the heavy phases removed from the plant and enters the extraction column 56 where it meets the solvent mixture entering through valve 57. The selectivity of the solvent mixture has been adjusted by the modus of operation of the stripper 76 as will be described later and its temperature has been regulated by the cooler 78 to the operating temperature chosen for column 56.

The extraction residue from column 56 forms a heavy liquid phase which is withdrawn through valve 58. The solvent mixture dissolved therein contains a considerably greater proportion of the less volatile constituent than the circulating solvent mixture entering through valve 57. It is evaporated from the oil traction F in apparatus not shown for the sake of simplicity in FIG. 2 and is returned eventually to tanks 51 and 81 respectively. The apparatus and operations for solvent recovery from all fractions I -F not shown are analogous to the devices 17-22 and 17a-22a respectively of FIG. 1 and operations described above.

The extract formed in column 56 is pumped by pump 59 to the pressure chosen for the precipitation operation and passes through the heater 60 in which the oil dissolved in the extract is precipitated by increase of temperature. The resulting suspension of precipitate in solvent mixture passes on to the mixer 61 into which an additional amount of the more volatile solvent constituent is admitted through valve 62 from tank 81. The rate of this addition is adjusted to result in the desired selectivity of the solvent mixture for column 56a. suspension is then passed to the separator 63 where the precipitated heavy phase is allowed to settle and is partly refluxed by valve 65 to column 56, partly passed on by valve 66 for into the middle of column 56a. The temperature of this heavy phase can be reduced by cooler 64.

By the operation described the lighter phase has been freed from dissolved oil to such an extent that it can be used as solvent mixture in the next extraction state, i.e. in column 56a. This solvent mixture now contains a still greater excess of the more volatile solvent constituent than that which has been caused by withdrawal of the heavy liquid layers through valves 58, 65, and 66 containing a greater proportion of less volatile solvent. In order to adjust the selectivity of the solvent mixture to the value desired in column 56a two means are available, i.e. the rate of more volatile constituent admitted to the mixer 61 and the temperature of operation of column 56a. The latter is regulated by the cooler 67.

The operation of column 56a and its accessory equipment 57a-67a is exactly analogous to the operation of column 56 and its accessory equipment described above. The only dilferences are:

(a) The solvent power of the solvent is reduced and thereby its selectivity increased as compared with that The used in column 56. This is accomplished by an increased content of the more volatile solvent constituent and, if desired, by increased operating temperature.

(b) The saturator 61a is placed before the heater 60a, i.e. the order of these devices is reversed. The combined effect of both devices, however, is the same, irrespective of the order.

The bottom product of column 56a yields the fraction F The top product of column 560 is partly used as reflux for column 56a partly passed on to column 68 for further fractionation. The essentially oil-free solvent mixture recovered from the extract in separator 63a is admitted through valve 571') into column 68. The operation of column 63 itself is analogous to that of columns 56 and 56a the only difference being a still lower solvent power of the solvent mixture. The accessory devices of column 68, however, differ from the preceding columns. No additional amount of low boiling constituent is added to the extract. The precipitation is carried out by pumping the extract with pump 69 through the heater 70 where it is heated for precipitation of a heavy phase. The precipitated heavy liquid phase is allowed to settle in the separator 71. Part thereof is returned by valve 73 as reflux to column 68 while the other part is withdrawn by valve 74 for recovery of fraction F in the manner described for FIG. 1. The heavy phase may be cooled in cooler 72 to the operating temperature of column 68 if desired.

The lighter phase from the separator 71 is expanded through valve 75 into the stripper 76 provided with heating means 77 and dephlegmator 79. If the stripper 76 can be operated at a higher pressure than that prevailing in tank 81 the gaseous or vaporous light constituent of the solvent mixture is simply expanded by valve 80 into tank 81. However, if it is not possible or desirable to work the stripper at such a high pressure, e.g. if the pressure in 81 is beyond the critical pressure of the solvent mixture, valve 80 is closed, the pressure in the stripper is reduced to the desired value and the gas is expanded through valve 82 and compressed into tank 81 by the booster 84. By maintaining the pressure and temperature in stripper 76 at constant values the composition of the liquid solvent mixture leaving the stripper can be closely controlled and kept constant, irrespective of any momentary fluctuations arising from the operation of the preceding columns. The solvent mixture is cooled in cooler 78 to the operating temperature of column 56.

The extraction residue settling to the bottom of column 68 is withdrawn through valve 58b for recovery of fraction F in equipment not shown in FIG. 2.

The plant shown in FIG. 2 is designed for refiractionation of the top products of columns 56 and 56a. If instead the bottom products are to be refractionated it is necessary that the solvent mixture used in the first column has a higher solvent power than that used in the second column, and that the solvent power of the solvent mixture used in the third column is still higher. This can be achieved in several different manners. The simplest manner is to reverse the flow of the oil through the plant. In this case the solution of less volatile solvent constituent in the oil is passed from the mixer 55 into the middle of column 68 while the extraction residue from this column is passed from valve 58b to the middle of column 56a and the extraction residue from column 56a from valve 58a into the middle of column 56. The top products of all three columns and the bottom product of column 56 are withdrawn by valves 74, 66a, 66, and 58 respectively and after evaporation of the solvent contained in these products in equipment not shown they yield the desired fractions.

Another possible arrangement is to provide columns 56 and 56a with strippers analogous to 76 and only column 68 with a saturator analogous to 61. In this case the outlet valve 58 is connected with the middle of column 56a, valve 58a with the middle of column 66 and all top products together with the bottom product of column 68 are withdrawn for the recovery of fractions.

Anyone skilled in the art can devise suitable other combinations to suit the requirements of the material to be fractionated.

The following examples are given by way of illustration and not limitation:

EXAMPLE I Crude soap obtained by refining linseed oil with caustic soda lye according to the conventional continuous centrifuging process was acidified and the fatty acids thus liberated were washed with water, dried and filtered at elevated temperature.

This crude mixture, which still contained a considerable percentage of'glycerides, was fractionated in a plant according to FIG. 2 using technical propane-propylene (in the following called fpropane) as liquid solvent and methane 'as gas. 7

The crude was mixed in the mixer 55 with about an equal quantity of propane and this solution was introduced into the middle of column 56. The fractions F F and F were drawn 01f as bottom products from the columns 56, 56a and 68. Sufiiciently large parts of the top products'of columns 56, 56a and 68 were refluxed through the valves 65, 65a and 73 into the respective columns. The rest of the top product of column 56 was further fractionated in column 56a and the rest of the top product of the latter column in column 68. Only the top product of column 68 was withdrawn as fraction F In column 56 a solvent fraction with a saturation pressure of 45 atm. absolute was used. The working pressure was maintained at 50 atm. gauge and the working temperature at 20 C. The reflux ratio was 3:1. The residue of extraction was withdrawn from the bottom of the column as fraction F and freed from solvent by distillation in the usual manner. The extract was pumped to 80 atm. gauge by pump 59 and heated to 60 C. in heater 60. A sufi'lcient quantity of methane was added to the mixer 61 as to obtain such a saturation pressure of the solvent that, after cooling to 20 C. in the cooler 67, it amounted to 55 atm. absolute. The lower layer collected in separator 63 was cooled in cooler 64 to 20 C. and that part thereof which was not used for reflux to column 56a was passed on to the middle of column 56a by valve 66. The working pressure of column 56a was maintained at 60 atm. gauge, the temperature at 20 C. and the reflux ratio at :1. The extraction residue was withdrawn as fraction F5 through valve 58a. The extract was precipitated at 90 atm. gauge. The quantity of methane added to the mixer 61a was adjusted so that the saturation pressure of the solvent after being cooled in cooler 67a was 67 atm. absolute, suitable for extraction in column 68. In order to'complete the precipitation the extract was heated in heater 60a to 45 C. The top product of column 56;: thus precipitated was partly applied as reflux to column 56a,'pa'rtly passed through valve 66:: to the middle of column '68, which waskept at 71 atm. gauge. The reflux ratio for column 68 was maintained at 5:1 and/the residue of the extraction was withdrawn as fraction F through valve 58b.

The extract was pumped from the top of column 68 by pump 69 to 90 atm. gauge and was precipitated by heatring in heater 70 to 50 C. 'This temperature exceeded the critical temperature of the solvent mixture which possessed the saturation pressure mentioned of 67 atm. at C. 'Ihe solvent mixture freed from oil in the separator 71 was expanded through-valve 75 into stripper 76 maintained at 55 atm. gauge. Valve 75 kept the pressure diflerence of atm. automatically constant between the separator 71 and the stripper 76. Valve 82 was adjusted so that it kept a constant pressure of 55 atmfgauge in the stripper 76. The gas released through the dephlegma tor 79 was recompressed by compressor 84 into conmethane.

around 46 atm. gauge.

'tainer 81 in which the pressure was automatically maintained between and atm. gauge, while the liquid solvent mixture which had a saturation pressure of 45 atm. abs. at 20 C. was reused in column 56. The fractions F to F were freed from the solvent mixture in the same manner as described for FIG. 1 and the solvent components were returned to containers 51 and 81 respectively. I,

The properties of the crude and of the various fractions are shown in Table 1.

Table 1 Crude F1 13' F F4 mixture 167 106 234 105 193 148 186 203 205 144 70 25 '200 203 Color (Gardner) Brown- Black 12 5 2 V black EXAMPLE II In a plant according to FIG. 3 crude linseed oil was fractionated using a solvent mixture of propane and All three columns were operated at 20 C.

The solvent mixture applied in column 156 had a saturation pressure of 30 atm. abs. The operating pressure was 33 atm. gauge. Fraction F was Withdrawn from the bottom of this column. The top product was refractionated in column 168 at an operating pressure of 38 atm. gauge using a solvent mixture with a saturation pressure of 35 atm. abs. The top product of column 168 was Withdrawn as fraction F while; the bottom product of this column, amounting to the greatest part of the linseed oil, was separated into two further fractions F and F in column 156a at an operating pressure of 36 atm. gauge with a solvent mixture possessing a saturation pressure of 33 atm. abs. The details of operation were analogous to those described in Example I with the exception that separator 171.could be operated at 50 atm. gauge which was considerably below the critical pressure of this mixture. Thus the stripper 176 could be operated'at practically the same pressure and the gas liberated through the dephlegmator 179 was expanded through valve 180 directly into the container 181 where the pressure was kept Valves 182 and 183 were kept closed and compressor 184 was not used. The results are shown in Table 2.

A refined mixture of linseed oil fatty acids which had been distilled twice under vacuum and had an iodine number of 179 was fractionated in an apparatus according to FIG. 1 using a mixture of acetone and carbon dioxide as solvent. 7 V p V The composition of the solventmixture in column 6 M was maintained at 13% acetone and 87%. carbonjdioxide.

It was changed to 7% actone and 93% carbon dioxide in mixer 9 and the precipitation of the extract was completed by. heating it to 70 C. in heater 12. The reflux which was notcooled in 14 was recirculated hot into column 6 while the rest of the precipitate was freed from CO and acetone in evaporator 17 and withdrawn through valve 19 as F This fraction had an iodine number of 189 while. the extraction residue was withdrawnthrough valve 30, freed from' the solvent mixture in evaporator 17a, and collected through valve 192. It had an iodine number of 162. This result shows that the solvent mixture acetonecarbon dioxide has the unexpected peculiarity of preferentially dissolving unsaturated compounds in contrast to the mixtures containing only hydrocarbons or hydrocarbons and carbon dioxide.

EXAMPLE IV A cat cracking recycle stock which had a relative carbon forming tendency of 7 was extracted in a 2 column plant consisting of 2 independent single columns fractionating units, -i.e. the solvent in each unit was circulated internally and not reused in the other. In the first fractionating unit propane only was used as solvent in a conventional manner as in deasphaltizing. An extraction residue amounting to about 25% by Wt. was removed as asphalt. The extract was precipitated by heating it considerably above the critical temperature of propane and the top product of the deasphaltizing column thus obtained was pumped into a fractionating unit according to FIG. 1. There it was extracted in column 6 with a solvent consisting of propane and methane possessing a saturation pressure of 85 atm. abs. and Working pressure of 90 atm. gauge. The extract was pumped by pump 8 to a pressure of 105 atm. abs. and methane added in the mixer 9 to a saturation pressure of 105 atm. abs. By increasing the temperature to 60 C. in heater 12, complete precipitation was achieved and the precipitate Withdrawn from the separator 13 was partly refluxed to column 6 partly withdrawn through valve 16 and freed from solvent in evaporator 17. The top product thus received had a relative carbon forming tendency below 1. The solvent layer was expanded into the stripper 26 and stripped to a saturation pressure of 85 atm. abs. at 20 C. and the gas was recomprssed to 110 atm. gauge in vessel 11.

This application is a continuation-in-part of my copending application Serial No. 45l,566, filed August 23, 1954 now Patent No. 3,098,034, July 16, 1963.

I claim:

1. In a process for the fractionation of high molecular weight organic material by liquid-liquid extraction in counter-current flow with a homogenous solvent mixture comprising at least one normally liquid solvent containing a predetermined amount of a gas dissolved therein followed by recovery of the extract from which the solvent, which is substantially freed of the extracted organic material by at least one of temperature increase and gas addition causing precipitation, the improvement which comprises regulating the selectivity of the solvent mixture for reuse by dissolving a further quantity of the gaseous solvent constituent in the solvent mixture at least at one point in the solvent mixture circuit outside of the extraction zone, and at another point of the solvent mixture circuit removing the said gaseous constituent from the solvent mixture and controlling the extent of at least one of said addition and removal of the gaseous constituent to thereby adjust the content of the dissolved gas in the solvent at a predetermined value for reuse and recycling the solvent for reuse.

2. Improvement according to claim 1 in which said extraction is a multi-stage extraction with the solvent in the difierent extraction stages having diiferent predetermined amounts of gas dissolved therein and in which the solvent after at least one extraction stage has its gas content adjusted by said control of the extent of at least one of said addition and removal to said predetermined amount for a different extraction stage and is recycled to said different extraction stage for reuse.

3. Improvement according to claim 2 in which said precipitation is eifected by temperature increase.

4. Improvement according to claim 1 in which the organic material is mixed with the liquid constituent of the solvent mixture and then purified prior to said extraction.

5. Improvement according to claim 1 in which said precipitation is effected by temperature increase.

6. Improvement according to claim 1 in which said solvent mixture comprises acetone having carbon dioxide dissolved therein.

7. In the process for the fractionation of higher molecular weight organic material by liquid-liquid extraction in counter-current flow with a homogenous solvent mixture comprising at least one normally liquid solvent containing a predetermined amount of gas therein, the improvement which comprises utilizing acetone having carbon dioxide dissolved therein as the solvent mixture.

References Cited by the Examiner UNITED STATES PATENTS 2,116,188 5/38 Churchill 208-323 2,130,147 9/38 Milmore 208317 2,188,012 l/40 Pilat et al. 208323 2,188,013 1/40 Pilat et al 208324 2,188,051 1/40 Lantz 208- 516 2,246,227 6/41 Nebb 208-323 3,098,034 7/63 Groll 208-316 FOREIGN PATENTS 156,694 7/63 Great Britain.

ALPHONSO D. SULLIVAN, Primary Examiner.

JAMES S. BAILEY, Examiner. 

1. IN A PROCESS FOR THE FRACTIONATION OF HIGH MOLECULAR WEIGHT ORGANIC MATERIAL BY LIQUID-LIQUID EXTRACTION IN COUNTER-CURRENT FLOW WITH A HOMOGENOUS SOLVENT MIXTURE COMPRISING AT LEAST ONE NORMALLY LIQUID SOLVENT CONTAINING A PREDETERMINED AMOUNT OF A GAS DISSOLVED THEREIN FOLLOWED BY RECOVERY OF THE EXTRACT FROM WHICH THE SOLVENT, WHICH IS SUBSTANTIALLY FREED OF THE EXTRACTED ORGANIC MATERIAL BY AT LEAST ONE OF TEMPERATURE INCREASE AND GAS ADDITION CAUSING PRECIPITATION, THE IMPROVEMENT WHICH COMPRISES REGULATING THE SELECTIVELY OF THE SOLVENT MIXTURE FOR REUSE BY DISSOLVING A FURTHER QUANTITY OF THE GASEOUS SOLVENT CONSTITUENT IN THE SOLVENT MIXTURE AT LEAST AT ONE POINT IN THE SOLVENT MIXTURE CIRCUIT OUTSIDE OF THE EXTRACTION ZONE, AND AT ANOTHER POINT OF THE SOLVENT MIXTURE CIRCUIT REMOVING THE SAID GASEOUS CONSTITUENT FROM THE SOLVENT MIXTURE AND CONTROLLING THE EXTENT OF AT LEAST ONE OF SAID ADDITION AND REMOVAL OF THE GASEOUS CONSTITUENT TO THEREBY ADJUST THE CONTENT OF THE DISSOLVED GAS IN THE SOLVENT AT A PREDETERMINED VALUE FOR REUSE AND RECYCLING THE SOLVENT FOR REUSE. 